1. Field of the Invention
The present invention relates to printed circuit board (PCB) antennas, and more particularly to a PCB antenna occupying a relatively small space.
2. Description of the Related Art
Microstrip PCB antennas are widely used in various mobile communications devices such as cellular phones. The trend toward miniaturization of mobile communications devices requires the size of a microstrip PCB antenna to become smaller and smaller, yet without compromising the functions of the antenna.
A conventional microstrip PCB antenna is disclosed in U.S. Pat. No. 6,295,029. The PCB antenna has a circuit board. A microstrip conductive line is printed on a face of the circuit board in the shape of a rectangular spiral. The microstrip conductive line has a length equal to one quarter of a wavelength (xcex) of a radio frequency signal to be used by a mobile communications device in which the microstrip PCB antenna is installed. An end of the rectangular spiral microstrip line is connected via a vertical section to a microstrip line. That microstrip line has a length equal to {fraction (1/20)} of xcex, and acts as an open-stub. A junction of the rectangular spiral microstrip conductive line and the open-stub acts as a signal feeder point. A ground plane is provided near the signal feeder point, but does not connect therewith. A hole is defined in the ground plane, so that the ground plane can obtain a desired harmonic oscillation frequency shifting. Unfortunately, all of the microstrip lines are disposed on the same face of the circuit board. Accordingly, the overall size of the PCB antenna is unduly large.
There exists a need for an improved microstrip PCB antenna that occupies a relatively small space in a corresponding mobile communications device.
It is an object of the present invention to provide a printed circuit board (PCB) antenna that occupies a relatively small space.
To achieve the above object, a microstrip PCB antenna in accordance with the present invention comprises a printed circuit board (PCB), a plurality of metal sheets and a plurality of microstrip traces. A plurality of antenna units is provided on the PCB. Each antenna unit comprises one metal sheet, and a plurality of microstrip traces. In each antenna unit, the metal sheet serves as a grounding plane and the microstrip traces serve as a signal unit. The microstrip traces are disposed on both top and bottom faces of the PCB. An end of each microstrip trace forms a conductive through hole defined in the PCB. Each conductive through hole electrically connects the microstrip trace with a corresponding microstrip trace disposed on an opposite face of the PCB. The conductive through holes are sequentially electrically connected together by the microstrip traces on the top and bottom faces of the PCB. All the microstrip traces and all the conductive through holes thereby form a continuous conductive line. Thus, a size of the antenna unit is significantly less than corresponding antenna units in conventional microstrip PCB antennas.
The invention will be described in more detail, by way of examples, with reference to the accompanying drawings in which: